The subject matter of this specification relates generally to image annotation.
Image search engines have become a popular tool on the Internet. These search engines help users find images that match their criteria. Some of these search engines index images by keywords or labels. Such image search engines retrieve images by matching users' search queries against these keywords or labels.
The keywords or labels for indexing an image can be drawn from text surrounding the image in a web page or other text associated with the image (e.g., the filename of the image, metadata associated with the image), for example. The keywords or labels can provide some indication of the content of an image. For example, an image of a horse can be associated with the keyword “horse.” In some cases, the keywords for an image that are extracted from the text may be uninformative or not useful. For example, words such as “cool” and “wow” generally are uninformative with regard to the content of an image. Poorly labeled images can degrade the quality of an image search result.